Splash art is a modification of a splash screen. A splash screen used to be (well, still is in some cases) a graphic along with a logo and sometimes the current version of the software involved. It was generally the screen that would be displayed while the software was loading when it first started up.
Splash art has evolved from this: it's no longer just to show the user the logo and what version of the software they're using, but instead is commonly used in games in between levels or on loading screens. It's especially common in games where you play individual matches (like LoL) or when there are a lot of load-screens between games.
A splash in comic books is a page used to grab the attention of the reader. It's usually a piece of art the covers the whole page rather than just a panel. This is used for introductions of characters, or the start of a new story, or a major event happening.
https://www.bing.com/images/search?q=Splash+art&form=HDRSC3&first=1 ↗️
